1. Field of Invention
This invention relates generally to improvements in continuously variable transmissions (CVTs) employed in vehicular applications. More particularly, the invention relates to an improved CVT that offers considerably reduced structural complexity compared to typical toroidal types of CVTs.
2. Description of the Prior Art
Automatically actuated electromechanical transmissions include actuation software modules of the embedded type, generally including connection links to engine control modules through standardized protocols. To the extent that the most new on-highway truck transmissions are actuated and controlled by software, they lend themselves to fully automated controls. As such, there has been considerable interest in providing CVT-like operating systems in trucks, motivated substantially by desire for improved economy of operation.
U.S. Pat. No. 6,085,606 issued Jul. 11, 2000 to Stine et al. provides an example of one such CVT-like transmission. That patent describes a 12-speed transmission which, although including gears, provides relatively small steps between the ratios of its highest ratio gears, gears 7-12, compared to the ratio steps between its lowest gears, 1-6. Thus, in its highest gear ratios, the behavior of the transmission approximates an actual CVT. Indeed, to the extent that on-highway trucks spend approximately 85-90 percent of their operating lives in their highest gear ratios, such accommodation involving only the highest gears has been deemed to be a suitable relatively inexpensive approach, though of course more limited than an actual CVT.
Thus, use of a CVT-like or xe2x80x9cmock CVTxe2x80x9d approach has been acceptable in that it generates significant benefits in fuel economy, while traditionally considerably cheaper to manufacture than significantly more expensive full CVT transmissions. Indeed, the presently emerging belt-type and toroidal CVT transmissions, even at today""s levels of technology and development, are believed to be insufficient to accommodate and/or transmit the relatively high torques associated with on-highway trucks. Thus, a full, actual CVT transmission for trucks that could be manufactured relatively inexpensively, and that could operationally meet required torque demands, would be well received, particularly among truck fleet owners.
A rotary cone-type continuously variable transmission (CVT) incorporates at least a pair of countershafts that are relatively rotatable within a transmission housing. The CVT is both beltless and non-toroidal, and includes at least two countershafts mounted within the housing in a manner so as to support controlled limited axial and pivotal movements thereof relative to the housing as well as to one another.
The axially translatable ends of each of the countershafts are entirely contained within the housing, and a first end of each countershaft has a greater diameter than its second end. A pair of axially spaced, radially floating transmission input and output cones is rotatably positioned within the housing along a shared longitudinal axis, the respective cones being arranged to rotate independently of each other while being axially fixed relative to one another between the at least two countershafts.
In the described embodiment, the greater diameter first ends of the two countershafts are defined by disks designed to bear against and to make rolling contact with one (the input) of the radially intermediately positioned cones, while the smaller second ends of the two countershafts are defined by smaller disks designed to bear against and make rolling contact with the second (output) cone.
The CVT as disclosed is deemed suitable for economical replacement of geared electromechanically actuated main transmission boxes of compound transmissions in at least medium duty truck transmission systems. As an example, one line-haul truck transmission consists of a five-speed main box and a separate auxiliary five-speed deep reduction box to provide 15 forward speed ratios. The replacement of the five-speed main box with the CVT unit of this invention would significantly enhance overall operating efficiency of the described 15-speed system.